should you wait for ATC to pass you a descent clearance?
Yes yes yes, but they are only human, if you are getting too close to reach a height requirement on the STAR issued, request descent, even then if it's too late, cause you didn't notice and the ATC did descend you in time, request a cancellation or amendment of the requirement as soon as you notice it ain't going to happen.
Many ATCs will assume (foolishly) you will make all the requirements and turns, it's part of the STAR; even if their clearance didn't enable you to comply.
When saying "We can't meet FL180 by 10 POINT", say what level you can reach as it will enable a better response from the ATC. I'd prefer "We can only meet FL195 by 10 POINT, <REASON> because of the late descent clearance, slowing up due turbulence", etc.